What term is used to describe transmission conductors that are paralleled together and fastened to the same support?

The term that describes transmission conductors that are paralleled together and fastened to the same support is "bundled conductor." Bundled conductors are used primarily to reduce electromagnetic interference and to improve the efficiency of power transmission. By grouping several conductors together, engineers can help reduce line losses and improve the electrical performance of the transmission system.

Bundled conductors are particularly popular in high-voltage transmission lines, where the increased surface area allows for better heat dissipation and reduced corona discharge. This configuration also helps to manage the mechanical stresses placed on the conductors and the supports, as multiple conductors working together provide greater strength than a single conductor alone.

In contrast, the other choices refer to different aspects of electrical transmission or support structures but do not accurately represent the concept of multiple conductors being paralleled and fastened together. Guard structures are protective systems, Kellum grips are specific types of clamps used for securing cables, and articulated running boards are used for worker safety on poles, none of which pertain to the description of bundled conductors.